#ifndef PIL_NotificationCenter_INCLUDED
#define PIL_NotificationCenter_INCLUDED


#include "../Environment.h"
#include "Notification.h"
#include "Mutex.h"
#include "../Types/SharedPtr.h"
#include <vector>
#include <cstddef>

namespace pi {

class AbstractObserver;


class PIL_API NotificationCenter
    /// A NotificationCenter is essentially a notification dispatcher.
    /// It notifies all observers of notifications meeting specific criteria.
    /// This information is encapsulated in Notification objects.
    /// Client objects register themselves with the notification center as observers of
    /// specific notifications posted by other objects. When an event occurs, an object
    /// posts an appropriate notification to the notification center. The notification
    /// center invokes the registered method on each matching observer, passing the notification
    /// as argument.
    ///
    /// The order in which observers receive notifications is undefined.
    /// It is possible for the posting object and the observing object to be the same.
    /// The NotificationCenter delivers notifications to observers synchronously.
    /// In other words the postNotification() method does not return until all observers have
    /// received and processed the notification.
    /// If an observer throws an exception while handling a notification, the NotificationCenter
    /// stops dispatching the notification and postNotification() rethrows the exception.
    ///
    /// In a multithreaded scenario, notifications are always delivered in the thread in which the
    /// notification was posted, which may not be the same thread in which an observer registered itself.
    ///
    /// The NotificationCenter class is basically a C++ implementation of the NSNotificationCenter class
    /// found in Apple's Cocoa (or OpenStep).
    ///
    /// While handling a notification, an observer can unregister itself from the notification center,
    /// or it can register or unregister other observers. Observers added during a dispatch cycle
    /// will not receive the current notification.
    ///
    /// The method receiving the notification must be implemented as
    ///     void handleNotification(MyNotification* pNf);
    /// The handler method gets co-ownership of the Notification object
    /// and must release it when done. This is best done with an AutoPtr:
    ///     void MyClass::handleNotification(MyNotification* pNf)
    ///     {
    ///         AutoPtr<MyNotification> nf(pNf);
    ///         ...
    ///     }
    ///
    /// Alternatively, the NObserver class template can be used to register a callback
    /// method. In this case, the callback method receives the Notification in an
    /// AutoPtr and thus does not have to deal with object ownership issues:
    ///     void MyClass::handleNotification(const AutoPtr<MyNotification>& pNf)
    ///     {
    ///         ...
    ///     }
{
public:
    NotificationCenter();
        /// Creates the NotificationCenter.

    ~NotificationCenter();
        /// Destroys the NotificationCenter.

    void addObserver(const AbstractObserver& observer);
        /// Registers an observer with the NotificationCenter.
        /// Usage:
        ///     Observer<MyClass, MyNotification> obs(*this, &MyClass::handleNotification);
        ///     notificationCenter.addObserver(obs);
        ///
        /// Alternatively, the NObserver template class can be used instead of Observer.

    void removeObserver(const AbstractObserver& observer);
        /// Unregisters an observer with the NotificationCenter.

    bool hasObserver(const AbstractObserver& observer) const;
        /// Returns true if the observer is registered with this NotificationCenter.

    void postNotification(Notification::Ptr pNotification);
        /// Posts a notification to the NotificationCenter.
        /// The NotificationCenter then delivers the notification
        /// to all interested observers.
        /// If an observer throws an exception, dispatching terminates
        /// and the exception is rethrown to the caller.
        /// Ownership of the notification object is claimed and the
        /// notification is released before returning. Therefore,
        /// a call like
        ///    notificationCenter.postNotification(new MyNotification);
        /// does not result in a memory leak.

    bool hasObservers() const;
        /// Returns true iff there is at least one registered observer.
        ///
        /// Can be used to improve performance if an expensive notification
        /// shall only be created and posted if there are any observers.

    std::size_t countObservers() const;
        /// Returns the number of registered observers.

    static NotificationCenter& defaultCenter();
        /// Returns a reference to the default
        /// NotificationCenter.

private:
    typedef SharedPtr<AbstractObserver> AbstractObserverPtr;
    typedef std::vector<AbstractObserverPtr> ObserverList;

    ObserverList  _observers;
    mutable Mutex _mutex;
};


} // namespace pi


#endif // PIL_NotificationCenter_INCLUDED
